But Goku expected to fight a Ssjin3 tier, that's why he need to trained for a rematch. And he said he just met his expectation.
So he's been training for Pure Boo's reincarnation. Its really stupid if he's expecting him to be just a Ssjin2 tier.
Chapter: 518 (DBZ 324), P11.6-8
Goku: “He’s the one…While I’ve been training on my own, I’ve been waiting all this time for that kid to enter the tournament…[ ]…10 years ago, when that outrageously bad Majin Boo died, I made a wish…That this time, he be reborn as a good guy, so we could fight one-on-one…Apparently old man Enma Daio heard me, and pulled some strings on my behalf…â€
Chapter: 519 (DBZ 325), P12.2-5
Context: Oob is surprised by Goku’s Bukujutsu
Goku: “Oh, I see. You still don’t even know how to fly, huh? …I guess there ain’t no helping it. You haven’t had no teacher, and you probably never even considered things like that. Sorry I bad-mouthed you before. Please forgive me. I just wanted to know your true ability. You’re exactly the person I thought you were. As amazin’ as I expected. But you don’t know how to use your power. This is the first time you’ve fought like this, right? I've got it! From now on I'll live with you at your house and teach you